1. Field of the Invention
One or more aspects of the present invention generally relate to backlit displays and, more particularly, to reducing power consumption of backlit displays by reducing an amount of backlighting.
2. Description of the Related Art
Liquid crystal display (LCD) screens used in notebook computers are commonly backlit to make them easier to read. FIG. 1 illustrates an exemplary backlit liquid crystal display (LCD) 100 that includes a core of LCD material 102 between sheets of glass 104 and 106. A backlighting element 108 produces light to illuminate LCD material 102. As illustrated by the arrows, light produced by backlighting element 108 is generally diffuse, with components traveling in different directions. The light from backlighting element 108 is typically passed through a polarizer 110 that blocks light that is not aligned with an axis of polarization of polarizer 110. The light that is aligned with the axis of polarization is allowed to pass through the polarizer 110 for passing through LCD material 102.
The LCD material 102, has electro-optic properties that cause the polarization of light which passes through the LCD material 102 to twist. This twisting may be controlled by applying a voltage waveform to the LCD material 102 for each pixel in an array of pixels. Typically, an electronic circuit that controls the array of pixels operates by accepting a digital control value for each pixel in the array of pixels. The control circuit will apply a voltage waveform to the LCD material 102 for a pixel based on the digital control value for the pixel. Generally, the control circuit is configured so that smaller digital control values result in application of a voltage waveform which causes the LCD material 102 to twist the light in such a way that more of the light it is blocked by the second polarizer 112, causing the pixel to appear darker. Conversely, larger digital control values result in application of a voltage waveform which causes the LCD material 102 to twist the light in such a way that less of the light it is blocked by the second polarizer 112, causing the pixel to appear brighter.
From a power consumption standpoint, LCD backlighting may be far from efficient. For example, while the backlighting element 108 may be set to a bright level to illuminate the LCD material 102, depending on the digital values of pixels to be displayed, the LCD material 102 may be in a twisting configuration which causes a substantial portion of the light passing through the LCD material 102 to be blocked by the second polarizer 112. In particular, cinematic lighting used in movies may result in a relatively dim screen overall, resulting in an inefficient use of backlighting. Thus, LCD backlighting may be particularly inefficient when viewing movies, such as DVD movies, on an LCD screen of a notebook computer. In fact, power consumption of a backlit LCD may account for a large portion of overall power consumption of a notebook computer. The inefficiencies due to LCD backlighting may lead to reduced battery life, which may be particularly problematic, for example, when viewing DVD movies on long airline flights.
Conventional approaches to reducing power consumption of a backlit LCD are typically limited to reducing an amount of backlighting (i.e., dimming). For example, a notebook computer may be configured to dim the backlighting in response to detecting a power supply has been unplugged from an AC power supply and that the notebook is being powered from a battery. However, by dimming the backlighting without adjusting pixel values to compensate for dimming the backlighting, the overall brightness of the LCD, as perceived by a user, may be undesirably reduced.
Accordingly, a need exists for an improved method and apparatus for reducing power of backlit displays while maintaining an overall perceptible level of brightness of the display.